Abstract: The viscosity of slurry, which was made of Shenhua coal with bimodal distribution of particle size, was analyzed in detail. The effect of particle size ratio (λ) and different particle size volume fraction (ξ) were examined. An empirical correlation of slurry viscosity based on the experiment results was proposed. The results show that preparation the coal slurry with bimodal distribution of particle size can effectively reduce the viscosity of slurry and improve its volume fraction (Φ). With the same volume fraction, the viscosity of slurry rapidly declines as increasing particle size ratio. The viscosity of slurry is the smallest when the volume fraction of small particle is 35%. The maximum volume fraction calculated using Ouchiyama model is in agreement with the experimental values. The intrinsic viscosity [μ] keeps at constant value. If the effects of λ and ξ are fully taken into account in the maximum volume fractionΦ_m, the correlation of viscosity for single-peak distributed slurry could be used to predict that of bimodal distributed slurry.